Grass and vegetation mowing equipment may use one or more rotary cutting blades attached to vertically oriented spindles and suspended under a deck. The blade may be fastened to the bottom end of a spindle by a threaded bolt that extends through a mounting hole in the blade, or a nut may be fastened to the threaded end of the spindle. However, the bolt or nut may tighten or loosen during normal use. This may occur when the mower drive engages the spindle, or if the blade impacts an object during operation. If the bolt or nut tightens during use, it may become difficult to remove the blade from the spindle for service. If the bolt or nut loosens during use, there is a risk that the blade will cause injury or damage.
Several mower blade joint designs also have locked the blade to the spindle or provided an adapter to help lock the blade to the spindle. For example, U.S. Pat. No. 3,465,508 entitled Power Transmitting Means relates to a universal adapter in which the spindle or driving member is elliptical, square, or star-shaped. U.S. Pat. No. 3,564,824 entitled Rotary Mower Blade relates to a blade and adapter having a circular mounting hole with four opposing notches. U.S. Pat. No. 4,302,878 entitled Cutting Blade relates to a blade having a mounting hole with a plurality of inwardly extending wedge or trapezoidal shape members. U.S. Pat. No. 4,936,884 entitled Grass Cutting Device relates to a toothed retainer that fits into a notched mounting hole in the blade. U.S. Pat. Nos. 5,284,006 and 5,473,873, both entitled Combination Mower Blade, relate to a mower blade having a mounting hole with five petal-like keyways that engage matching keys of the shaft. U.S. Pat. No. 5,454,216 entitled Spindle For Mower Deck relates to a spindle having a raised section formed into a six-pointed toothed star. U.S. Pat. No. 5,724,796 entitled Mowing Blade With Star relates to a blade adapter with an asymmetrical star section. U.S. Pat. No. 5,881,540 entitled Mounting Member For Mower Blade Spindle relates to a spindle having a threaded portion and a raised section with a six-pointed toothed star shape. U.S. Pat. No. 5,946,895 entitled Adapter For Mowing Blade With Star relates to a blade adapter having a circular central section with four protruding asymmetrical teeth.
Several problems have been encountered with existing mower blade locking joints. The teeth or splines on the spindle and/or blade mounting hole may lack sufficient strength to withstand high impact forces if the mower blade strikes a stationary or solid object. Insufficient strength of prior art mower blade locking joints may be due, at least in part, to low contact area between the teeth or splines of the spindle and the blade mounting hole. Contact area also may be low if the blade is rotated slightly with respect to the spindle, or if there is a slight mismatch in the tooth profile of the spindle and that of the mower blade mounting hole. The spindle teeth or splines may yield before the mower blade because the spindle has lower hardness than the mower blade.
Additionally, the cross sectional area of the teeth or splines on a spindle may be smaller within the contact region of the joint than the cross sectional area of the mower blade. As a result, the teeth or splines on the spindle may yield or distort, and in some cases may shear off. This can make it difficult to remove or install the mower blades for service. If the teeth or splines become damaged or shear off, the joint may lose the locking capability to prevent the blade from turning relative to the spindle bolt.
An improved mower blade locking joint is needed to lock the mower blade to the spindle. An improved mower blade locking joint is needed to prevent the blade from rotating relative to the spindle bolt, and to prevent over-tightening or loosening of the joint during operation. A mower blade locking joint is needed that simplifies blade removal and installation for service. A mower blade locking joint is needed that provides higher strength to withstand impact forces if the mower blade strikes an object. A mower blade locking joint is needed without teeth or splines that may yield, distort, or shear off.